Latch switches At some point, i needed a switch that would stay on and off using just a pushbutton switch that only has a temporary contact.
So what i wanted:
The switch functions like: i push, it makes contact. I release, it opens.
But the endresult should be:
push (and release): a signal goes on and stays on
push again (and release): the signal is switched off

Something like this seems to be called a soft switch circuit, and there's a lot of solutions to the problem. My problem with most of them:

• They aren't rated for 5 or 12 volt, i hardly ever mess with 220V here except by using a relay, seperating high and low voltage very nicely.
• They tend to be over-engineered.. i just want to switch a relay on and off.
• They used exotic, expensive components.
• They used a lot of components, so stuffing it in something like a relay housing as a replacement is near impossible

Solution #1: 555 timer
A solution that works for alsorts of low voltage applications from 5 to 15V: use a 555 timer chip, in a different setup.
A 555 really is nothing more than a comparator circuit and a D-latch, which can be used for this purpose. See the schematic how this is accomplished.
The startup select jumper is used to set the initial state when the circuit powers up.